Under modern day industrial technology and practice, computer controlled, high-speed, mobile machine centers or "robots" capable of driving and positioning a variety of machine tools in selected spacial positions have gained popular acceptance for a wide variety of industrial applications. Such robots are capable in many instances of substantially unmanned automatic operation, including the ability to automatically change tooling whereby to carry out a host of pre-programmed machining operations such as drilling, milling, cutting, grinding, impacting, routing, measuring, fastener installation, inspecting, locating and other related tasks.
Robotic machines of this order must be highly accurate in positioning and operating the selected tooling and as a consequence they are generally heavy, relatively cumbersome, rigid and costly structures which, however, are uniquely tireless and thus capable of substantially uninterrupted, dependable, highly accurate, economical and cost effective production of consistently high quality products.
One such industrial application familiar to the inventor hereof, is described in U.S. Pat. No. 4,885,836, issued Dec. 12, 1989, to the assignee of this application. As therein described, a pair of synchronized, computer controlled, robotic machining centers capable of automatically working and operating in mirror relationship on opposite sides of fixture held components to be assembled are utilized in a work cell environment for the production of aircraft sections, for example. By providing suitable tooling to the two robotic machine centers, the components of the assembly are structurally unified by the use of rivets and similar fasteners, with the robots carrying out the basic hole preparation, rivet installation and riveting cycles under the supervision of computers which work the robots in accordance with memory banked design data for the complete assembly.
In general the robotic machine centers or robots described in said patent are mounted in parallel aisles to run along elongated horizontal tracks or bedways in response to actuation of suitable power drives; each robot being of Cartesian structure with mutually perpendicular X, Y and Z axes, the X axis being defined by the machine's associated horizontal linear bedways; the Y axis being defined by a central vertical column which carries a horizontal, linearally moveable power ram defining the Z axis of movement. An articulated wrist or twist head is mounted at one end of the ram and comprises a pair of transverse rotary movement axes. The vertical column preferably is rotatable about its vertical axis for defining a third rotary axis. The twist head of each of the robots is designed to accept selected end effectors carrying specific tooling for accomplishing required tasks with such tooling being capable of linear extension and retraction movements in accordance with corresponding linear movements of a rotatably driven quill.
In a later U.S. Pat. No. 4,955,119 issued Sept. 11, 1990 and assigned to the assignee hereof, provision of a novel multi-task end effector attachment for the articulated twist head of a computer controlled robotic machining center of the order set out in the aforesaid U.S. Pat. No. 4,885,836 is disclosed. According to the invention of this later patent a single robotic machining center is capable of performing the functions of hole preparation, rivet or fastener insertion and installation by virtue of a single end effector having master and slave tool heads in opposing coaxial relationship which are capable of operating on opposite sides of fixture held work pieces to carry out requisite functions. With the improvement of U.S. Pat. No. 4,955,119, a single robot has the capability of servicing multiple fixture held work part assemblies by rotatably swinging the robot's horizontal ram about the upright pedestal's vertical axis so that the robot can alternately service parts to be assembled in adjacent work cell aisles.
Despite the obvious economic advantages of dedicating a single robot to multiple assemblies as briefly outlined above, swinging the ram horizontally about the vertical axis of the robot's pedestal is not only time consuming, but requires sufficient space in which to carry out the operation. Such space is not always readily available in the confines of the work cell and the fixture held work pieces, however. Thus there is a need for a more versatile robotic machining center capable of selectively positioning a robot's ram to permit operation of tooling carried thereby in adjacent aisles of a work cell. It is to such an improvement that the present invention is directed.